Commuters travelling in and out of St Albans are being warned of delays on one of Govia Thameslink’s busiest services due to a staff shortage.

Trains between Bedford and Brighton could be cancelled and revised at short notice.

Disruption is still ongoing.

Earlier safety checks between London St Pancras and St Albans have also had a knock-on effect for commuters.

Spokesman Roger Perkins said: “We apologise to our passengers for the disruption this morning on Thameslink.

“One of our trains was sprayed with graffiti and had to be pulled from service and there were issues with track in the tunnel north of Kentish Town which meant we had to caution our trains through at low speed and a signalling issue at Cricklewood, both following on from the weekend’s engineering work.

“There have also been some cancellations due to a general shortage of drivers. Normally we can cover this through drivers working rest days but this was unfortunately not possible this morning because of sickness.

“When we took over the franchise, in September, there were not enough drivers to carry out day-to-day operations without asking drivers to work rest days and we have 30 more services now to cover every day on Thameslink.

“We’re working flat out on one of the UK’s biggest recruitment and training programmes but it takes over a year to train a driver and there is no quick fix.”